Bonanno, 57, went to work for Foamex in mid-1995 as executive vice president of manufacturing. He became president and CEO in July 1997.
Foamex officials said Bonanno resigned to pursue a "private venture opportunity." He also resigned from Foamex's board of directors.
Company officials credited Bonanno for "building a culture dedicated to product innovation, customer service and continuous improvement."
Before going to Foamex, Bonanno worked for 30 years at Chrysler Corp., and left as general manager of international manufacturing operations.
Grove is also an international corporation, with plants in the United States, France, Germany, Singapore and China. It has more than 5,300 workers, including about 2,500 in Franklin County. Its corporate headquarters are in Shady Grove.
Stift, 56, is a native of Chicago. He earned his bachelor's and master's degrees from Loyola University there. He lives in Hagerstown with his wife. They have three grown children.
Stift said he has no immediate plans.
"This all happened so fast. It came as a surprise," Stift said, adding that he would like to stay in the area.
Stift said it is not unusual for new owners to bring in their own management team.
According a press release from Grove, the corporation, under Stift's leadership, became firmly established as a leader in the global market.
In 1995, Grove acquired Krupp Mobilkrane along with Delta Aerial Platforms in France.
"Grove Worldwide is firmly positioned as a world-class company. I am extremely proud of the management team and our 5,300 employees around the world," Stift said.
Grove was started as a producer of farm wagons in a rented garage in 1947 in Shady Grove by John L. Grove, his brother and a third partner.
Today, Grove designs and builds mobile hydraulic cranes, truck-mounted cranes and self-propelled aerial work platforms.
Last year, Grove reported revenues of $865 million.